Touch screen sensor and patterned substrate having overlaid micropatterns with low visibility

ABSTRACT

Presently described are articles such as antennas, EMI shields, and touch screen sensors as well as patterned substrates having overlaid micropatterns with low visibility. Also described are methods of determining the visibility of a patterned substrate. In one embodiment, a patterned substrate is described comprising a visible light transparent substrate; and at least two overlaid electrically conductive mesh micropatterns, wherein each mesh has a repeating cell geometry and the combination of overlaid micropatterns has a spatial contrast threshold at a distance of 30000 units of greater than −35 decibels.

CROSS REFERENCE TO RELATED APPLICATIONS

This application is a continuation of U.S. patent application Ser. No.13/148,369, filed Aug. 8, 2011, which is a national stage filing under35 U.S.C. 371 of PCT/US2010/025127, filed Feb. 24, 2010, which claimspriority to U.S. Provisional Application No. 61/237,673, filed Aug. 27,2009, and PCT/US2009/035250, filed Feb. 26, 2009, the disclosures ofwhich are incorporated by reference in their entirety herein.

BACKGROUND

Touch screen sensors detect the location of an object (e.g. a finger ora stylus) applied to the surface of a touch screen display or thelocation of an object positioned near the surface of a touch screendisplay. These sensors detect the location of the object along thesurface of the display, e.g. in the plane of a flat rectangular display.Examples of touch screen sensors include capacitive sensors, resistivesensors, and projected capacitive sensors. Such sensors includetransparent conductive elements that overlay the display. The elementsare combined with electronic components that use electrical signals toprobe the elements in order to determine the location of an object nearor in contact with the display.

Other components that can overlay a display and that include transparentconductive elements include electromagnetic interference (EMI) shieldsand antennas.

SUMMARY

It has been found that while a single conductive (e.g. mesh)micropattern on a transparent (e.g. plastic film) substrate can bevirtually undetectable to an unaided human eye of normal (20/20) vision,the placement of a second conductive (e.g. mesh) micropattern overlayingthe first micropattern can result in the combination of micropatterns(i.e. the composite pattern) being highly visible.

In some embodiments, articles such as antennas, EMI shields, andespecially touch screen sensors are described. The articles comprise avisible light transparent substrate; a first conductive micropatterncomprising linear traces defining a first open mesh of a repeating cellgeometry disposed on or in the visible light transparent substrate, anda second conductive micropattern comprising linear traces defining asecond open mesh of a repeating cell geometry electrically isolated fromthe first conductive micropattern. The first conductive micropattern andthe second conductive micropattern are overlaid.

In yet other embodiments, methods of determining the visibility of apatterned substrate are described. The methods comprise providing adigital image of a micropatterned substrate; and calculating the spatialcontrast threshold from the digital image by use of a mathematical modelfor foveal detection. Such method can be useful for evaluating anddesigning micropatterns and micropatterned substrates having aparticular (e.g. low) visibility without fabricating a physical sample.

In yet another embodiment, a patterned substrate is described comprisinga visible light transparent substrate; and at least two overlaidelectrically conductive mesh micropatterns, wherein each mesh has arepeating cell geometry and the combination of overlaid micropatternshas a spatial contrast threshold at a distance of 30000 units of greaterthan −35 decibels.

In each of these embodied articles and patterned substrates, theoverlaid micropatterns can exhibit low visibility by virtue of thedesign and arrangement of the first and second micropatterns relative toeach other.

In one embodiment, the second conductive micropattern overlays the firstconductive micropattern such that at least a portion of the lineartraces of the second conductive micropattern are non-parallel to thelinear traces of first conductive micropattern. In another embodiment,at least a portion of the second conductive micropattern has a differentcell geometry from the cell geometry of the first conductivemicropattern. In another embodiment, at least a portion of the secondconductive micropattern has a different cell dimension from the celldimension of the first conductive micropattern. Further, the design andarrangement of the first and second micropattern may result in theoverlaid micropatterns having two or more of these attributes.

In some favored embodiments, the first and second conductivemicropattern have the same geometry such as a (e.g. regular) hexagonalcell geometry. The second micropattern may be orientated at a bias angleranging from about 15 degrees to about 40 degrees relative to the firstmicropattern. The first and second conductive micropattern may differ incell dimension by a ratio up to 1:6. The linear traces preferably have aline width of less than 10 microns, and more preferably less than 5microns. The cell dimension of the first and second micropattern ispreferably no greater than 500 microns.

BRIEF DESCRIPTION OF THE DRAWINGS

The invention may be more completely understood in consideration of thefollowing detailed description of various embodiments of the inventionin connection with the accompanying drawings, in which:

FIG. 1 illustrates a schematic diagram of a touch screen sensor 100;

FIG. 2 illustrates a perspective view of a conductive visible lighttransparent region lying within a touch screen sensing area;

FIG. 3A is a scanning electron photomicrograph of the geometry for aregular hexagonal mesh (sometimes referred to as “hex” mesh) conductivemicropattern;

FIG. 3B is a scanning electron photomicrographs of the geometry for asquare mesh conductive micropattern;

FIGS. 4A and 4B are illustrations depicting open meshes of a repeatingcell geometry comprising a combination of square and octagonal cells;

FIGS. 5 a-5 i are illustrations depicting two layers of the same regularhexagonal mesh overlaid such that the second micropattern is orientatedrelative to the first micropattern at increasing angles, starting with 5degrees for FIG. 5 a and increasing respectively from FIGS. 5 a to 5 iin 5 degree increments;

FIG. 6 is an optical photomicrograph (reflection illumination) depictingtwo overlaid layers of a hexagonal metallic mesh having a cell diameterof 200 micrometers and a square mesh having a cell pitch in bothdirections (length and width of squares) of 80 micrometers, theconductive traces are approximately 2 micrometers in width;

FIG. 7 is an optical photomicrograph (transmission illumination) ofSample 5 depicting two overlaid layers of a regular hexagonal metallicmesh wherein one micropattern has a cell diameter of 200 micrometers,the other micropattern has a cell diameter of 300 micrometers, and thehexagonal meshes are rotated by an angle of 27 degrees with respect toeach other (i.e. the bias angle equals 27 degrees);

FIG. 8 illustrates the arrangement of layers that are laminated togetherto form one embodiment of the touch screen sensor, an X-Y grid typeprojected capacitive touch screen sensor;

FIG. 9 illustrates a portion of the conductor micropattern for theX-layer or the Y-layer of an embodiment of a touch screen sensoraccording to FIG. 8;

FIG. 10 illustrates a portion of the conductor micropattern illustratedin FIG. 9, the portion including two visible light transparentconductive mesh bars, each contacting a larger feature in the form of acontact pad, as well as electrically isolated conductive deposits in thespace between the contacted mesh bar regions;

FIGS. 11, 11 a, and 11 b illustrate various portions of a firstpatterned substrate;

FIGS. 12, 12 a, and 12 b illustrate various portions of a secondpatterned substrate;

FIG. 13 illustrates a projected capacitive touch screen transparentsensor element constructed from overlaying the first and secondpatterned substrates of FIGS. 11 and 12;

FIGS. 14-36 depict magnified illustrations of an area of approximately1.5 mm by 2.5 mm of the overlaid micropatterns samples. Such overlaidpattern portions are smaller than the sample size used for determiningthe contrast threshold. Except for the optical micrographs of FIGS. 6and 7, the figures are not necessarily to scale. Like numbers used inthe figures refer to like components. However, it will be understoodthat the use of a number to refer to a component in a given figure isnot intended to limit the component in another figure labeled with thesame number.

DETAILED DESCRIPTION

Presently described are touch screen sensors and micropatternedsubstrates that comprise a visible light transparent substrate and atleast two electrically conductive micropatterns disposed on or in thevisible light transparent substrate. In some embodiments, eachelectrically conductive micropattern is disposed on or in separatevisible light transparent substrates. In other embodiments, the at leasttwo electrically conductive micropattern are disposed on or in a singlevisible light transparent substrate such that the conductive patternsare electrically isolated. The micropatterns are overlaid and canexhibit low visibility by virtue of the design and arrangement of thefirst and second patterns relative to each other.

As used herein “micropattern” refers to an arrangement of dots, lines,filled shapes, or a combination thereof having a dimension (e.g. linewidth) of no greater than 1 mm. In preferred embodiments, thearrangement of dots, lines, filled shapes, or a combination thereof havea dimension (e.g. line width) of at least 0.5 microns and typically nogreater than 20 microns. The dimension of the micropattern features canvary depending on the micropattern selection. In some favoredembodiments, the micropattern feature dimension (e.g. line width) isless than 10, 9, 8, 7, 6, or 5 micrometers (e.g. 1-3 micrometers).

As used herein, “visible light transparent” refers to the level oftransmission of the unpatterned substrate or article comprising themicropatterned substrate being at least 60 percent transmissive to atleast one polarization state of visible light, where the percenttransmission is normalized to the intensity of the incident, optionallypolarized light. It is within the meaning of visible light transparentfor an article that transmits at least 60 percent of incident light toinclude microscopic features (e.g., dots, squares, or lines with minimumdimension, e.g. width, between 0.5 and 10 micrometers, or between 1 and5 micrometers) that block light locally to less than 80 percenttransmission (e.g., 0 percent); however, in such cases, for anapproximately equiaxed area including the microscopic feature andmeasuring 1000 times the minimum dimension of the microscopic feature inwidth, the average transmittance is greater than 60 percent. The term“visible” in connection with “visible light transparent” is modifyingthe term “light,” so as to specify the wavelength range of light forwhich the substrate or micropatterned article is transparent.

Common visible light transparent substrates include glass and polymericfilms. A polymeric “film” substrate is a polymer material in the form ofa flat sheet that is sufficiently flexible and strong to be processed ina roll-to-roll fashion. By roll-to-roll, what is meant is a processwhere material is wound onto or unwound from a support, as well asfurther processed in some way. Examples of further processes includecoating, slitting, blanking, and exposing to radiation, or the like.Polymeric films can be manufactured in a variety of thicknesses, rangingin general from about 5 μm to 1000 μm. In many embodiments, polymericfilm thicknesses range from about 25 μm to about 500 μm, or from about50 μm to about 250 μm, or from about 75 μm to about 200 μm. Roll-to-rollpolymeric films may have a width of at least 12 inches, 24 inches, 36inches, or 48 inches.

Presently described are overlaid conductive micropatterns that can beintegrated directly with materials or components of a display. Forexample, one or more overlaid conductive micropatterns may be depositedonto the color filter glass layer of a liquid crystal display. Asanother example, one or more overlaid conductive micropatterns may bedeposited onto the exit polarizing film or compensation film of a liquidcrystal display (LCD). As another example, one or more overlaidconductive micropatterns may be deposited onto a substrate that is incontact with electrophoretic media in a reflective electrophoretic (EP)display. As another example, one or more overlaid conductivemicropatterns may be deposited onto a glass or plastic substrate thatsupports material layers of an organic light emitting diode (OLED)display. Some of such implementations of the conductive micropatternsmay be described as “on-cell.”

The disclosure further relates to contact or proximity sensors for touchinput of information or instructions into electronic devices (e.g.,computers, cellular telephones, etc.) These sensors are visible lighttransparent and useful in direct combination with a display, overlayinga display element, and interfaced with a device that drives the display(as a “touch screen” sensor). The sensor element has a sheet like formand includes at least one electrically insulating visible lighttransparent substrate layer that supports a conductive material (e.g.,metal) that is patterned onto the surface of the substrate in a meshgeometry so as to generate a transparent conductive region that lieswithin the touch sensing area of the sensor. However, the first andsecond conductive micropattern may have other arrangements provided thatthe second conductive micropattern (e.g. orthogonal to the first) iselectrically isolated from the first conductive micropattern. Forexample, an insulating component can be provided at the intersectionsbetween the first and second conductive micropatterns, as known in theart. It is within the scope of two conductive micropatterns that areelectrically isolated for the micropatterns both to be connected to thesame signal processing, logic, memory, or other circuitry for thepurpose of using the micropatterns as part of a system (e.g., drivingthe conductive micropatterns with electrical signals for the purpose ofcapacitively detecting the presence or location of a touch event to aninformation display). To be electrically isolated, the micropatternsneed only be lacking electrical contact in an overlapping or overlaidregion, by means of an insulating space (e.g., air, dielectric material)between them.

In the case of touch sensors comprising the conductive micropatterns, atleast a portion of the metal micropattern is contiguous and inelectrical connection with circuitry of an electronic illuminateddisplay.

The sensing area of a touch sensor for an information display is thatregion of the sensor that is intended to overlay, or that overlays, aviewable portion of the information display and is visible lighttransparent in order to allow viewability of the information display.Viewable portion of the information display refers to that portion of aninformation display that has changeable information content, e.g. theportion of a display “screen” that is occupied by pixels, e.g. thepixels of a liquid crystal display.

The touch screen sensors may be for example a resistive, capacitive, andprojected capacitive types. The visible light transparent conductormicropatterns are particularly useful for projected capacitive touchscreen sensors that are integrated with electronic displays. As acomponent of (e.g. projected capacitive) touch screen sensors, thevisible light transparent conductive micropattern are useful forenabling high touch sensitivity, multi-touch detection, and stylusinput.

While the present invention is not so limited, an appreciation ofvarious aspects of the invention will be gained through a discussion ofthe examples provided below.

FIG. 1 illustrates a schematic diagram of a touch screen sensor 100. Thetouch screen sensor 100 includes a touch screen panel 110 having a touchsensing area 105. The touch sensing area 105 is electrically coupled toa touch sensor drive device 120. The touch screen panel 110 isincorporated into a display device.

FIG. 2 illustrates a perspective view of a conductive visible lighttransparent region 101 that would lie within a touch sensing area of atouch screen panel, e.g., touch sensing area 105 in FIG. 1. Theconductive visible light transparent region 101 includes a visible lighttransparent substrate 130 and an electrically conductive micropattern140 disposed on or in the visible light transparent substrate 130. Thevisible light transparent substrate 130 includes a major surface 132 andis electrically insulating. The visible light transparent substrate 130can be formed of any useful electrically insulating material such as,e.g., glass or polymer. Examples of useful polymers for lighttransparent substrate 130 include polyethylene terephthalate (PET),polycarbonate (PC), polycarbonate co-polymers, and polyethylenenaphthalate (PEN). The electrically conductive micropattern 140 can beformed of a plurality of linear metallic features.

FIG. 2 also illustrates an axis system for use in describing theconductive visible light transparent region 101 that would lie within atouch sensing area of a touch screen panel. Generally, for displaydevices, the x and y axes correspond to the width and length of thedisplay and the z axis is typically along the thickness (i.e., height)direction of a display. This convention will be used throughout, unlessotherwise stated. In the axis system of FIG. 2, the x axis and y axisare defined to be parallel to a major surface 132 of the visible lighttransparent substrate 130 and may correspond to width and lengthdirections of a square or rectangular surface. The z axis isperpendicular to that major surface and is typically along the thicknessdirection of the visible light transparent substrate 130. A width of theplurality of linear metallic features that form the electricallyconductive micropattern 140 correspond to an x-direction distance forthe parallel linear metallic features that extend linearly along the yaxis and a y-direction distance for the orthogonal linear metallicfeatures correspond to a width of the orthogonal linear metallicfeatures. A thickness or height of the linear metallic featurescorresponds to a z-direction distance.

In the illustrated embodiment, the conductive visible light transparentregion 101 that lies within a touch sensing area of a touch screen panelincludes two or more layers of visible light transparent substrate 130each having a conductive micropattern 140.

The conductive micropattern 140 is deposited on the major surface 132.Because the sensor is to be interfaced with a display to form a touchscreen display, or touch panel display, the substrate 130 is visiblelight transparent and substantially planar. The substrate and the sensormay be substantially planar and flexible. By visible light transparent,what is meant is that information (e.g., text, images, or figures) thatis rendered by the display can be viewed through the touch sensor. Theviewability and transparency can be achieved for touch sensors includingconductors in the form of a deposited metal, even metal that isdeposited with thickness great enough to block light, if the metal isdeposited in an appropriate micropattern.

The conductive micropattern 140 includes at least one visible lighttransparent conductive region overlaying a viewable portion of thedisplay that renders information. By visible light transparentconductive, what is meant is that the portion of the display can beviewed through the region of conductive micropattern and that the regionof micropattern is electrically conductive in the plane of the pattern,or stated differently, along the major surface of the substrate ontowhich the conductive micropattern is deposited and to which it isadjacent.

In some embodiments, the articles described herein comprise a firstconductive micropattern comprising linear traces defining a first openmesh of a repeating cell geometry disposed on or in the visible lighttransparent substrate and a second conductive micropattern comprisinglinear traces defining a second open mesh of a repeating cell geometryelectrically isolated from the first conductive micropattern. The secondconductive micropattern may be disposed on the same substrate as thefirst conductive micropattern, or it may be disposed on anothersubstrate. The second conductive micropattern overlays the firstconductive micropattern in particular arrangements as will be described.

In some embodiments, both conductive micropatterns form at least aportion of a touch sensor, for example a touch screen sensor, as justdescribed.

Alternatively, in another embodiment, one of the conductivemicropatterns forms at least a portion of a touch sensor, for example atouch screen sensor, and the other conductive micropattern may functionas an antenna for wireless communication.

In yet another embodiment, one of the conductive micropatterns forms atleast a portion of a touch sensor, for example a touch screen sensor,and the other conductive micropattern may function as an electromagneticinterference (EMI) shield.

In yet another embodiment, one of the conductive micropatterns forms atleast a portion of an antenna for wireless communication and the otherconductive micropattern may function as an electromagnetic interference(EMI) shield.

Preferred conductive micropatterns include regions with two dimensionalmeshes (or simply, meshes), where a plurality of linear micropatternfeatures (often referred to as conductor traces or metal traces) such asmicropatterned lines define enclosed open areas within the mesh. Theopen areas defined by the (e.g. metal) micropattern can be described ascells such as square geometry cells, as depicted in FIG. 3B, and (i.e.regular) hexagon geometry cells, as depicted in FIG. 3A.

The first and second conductive micropatterns generally comprise lineartraces defining an open mesh of a repeating cell geometry. By repeatingcell geometry, it is meant that the micropattern has translationalsymmetry. Although FIGS. 3A and 3B depict cell designs having array ofcells wherein the cells have the same dimension and same cell geometry,the conductive micropattern may also have a repeating cell geometry thatcomprises two or more different cell geometries. For, example FIGS. 4Aand 4B are illustrations depicting an open mesh of a repeating cellgeometry wherein the repeat segment comprises a combination of a squarecell and an octagonal cell. Typically, the micropattern repeats over arelatively short distance. In some embodiments, the repeat segmentcomprises no greater than 2 or 3 cells. Although the depicted openmeshes include various arrangements of polygonal cell geometries withstraight line borders, the cells may also be defined by wavy orirregular linear traces, provided that the cells form a micropatternhaving a repeating pattern. Hence, it is within the scope of thisdisclosure for a repeating cell geometry to include multiple cellshaving different geometries and/or different sizes, provided that arepeat segment (or primitive) is present that can be translated in atleast one direction for at least a portion of the overall mesh orconductive micropattern.

As used herein, the geometry of a cell refers to its shape, and isdistinguished from its dimension(s). Cell geometries include squares,non-square rectangles, hexagons, octagons, other polygons, or otherfree-form shapes. A regular hexagon has a different shape than anon-regular hexagon wherein at least one of the edges has a differentlength from another edge or at least one included angle is not equal to120 degrees. When two cells have both the same shape and same dimension,the cells can be superimposed onto one another.

In some embodiments, either the first or the second micropatterncomprises a (e.g. repeating) pattern of cells having a regular cellgeometry. In some embodiments, both the first and the secondmicropattern comprise a (e.g. repeating) pattern of cells having aregular cell geometry. In some embodiments, both the first and secondmicropattern comprise cells having the same regular cell geometry. Byregular cell geometry, it is meant that the cells of the micropatternhave the shape of a regular polygon. A regular polygon has all edges ofequal length and all included angles of equal magnitude.

In some embodiments, the conductive traces defining the conductivemicropattern are designed not to include segments that are approximatelystraight for a distance greater than the combined edge length of fiveadjacent cells, preferably four adjacent cells, more preferably threeadjacent cells, even more preferably two adjacent cells. Mostpreferably, the traces defining the micropattern are designed not toinclude segments that are straight for a distance greater than the edgelength of a single cell. Accordingly, in some embodiments, the tracesthat define the micropattern are not straight over long distances, e.g.,10 centimeters, 1 centimeter, or even 1 millimeter. Patterns withminimal lengths of straight line segments, as just described, areparticularly useful for touch screen sensors with the advantage ofcausing minimal disturbance of display viewability.

In some embodiments, the first and second micropatterns each comprise asquare mesh. In other embodiments, one of the micropatterns comprises asquare mesh and the other micropattern a (e.g. regular) hexagonal mesh.Preferred overlaid conductive micropatterns comprise a first and secondmicropattern region with two dimensional contiguous (e.g. metal) meshes,wherein at least a portion of the linear traces that form the mesh arenon-parallel, such as certain polygonal networks such as (e.g. regular)triangular, pentagonal, and (e.g. regular) hexagonal networks. Morepreferably, the first and second micropatterns each comprise a (e.g.regular) hexagonal mesh.

The two-dimensional geometry of the conductive micropattern (that is,geometry of the pattern in the plane or along the major surface of thesubstrate) can be designed, with consideration of the optical andelectrical properties of the conductor material, to achieve specialtransparent conductive properties that are useful in touch screensensors.

Appropriate micropatterns of conductor for achieving transparency of thesensor and viewability of a display through the sensor have certainattributes. First of all, regions of the conductive micropattern throughwhich the display is to be viewed should have an area fraction of thesensor that is shadowed by the conductor of less than 50%, or less than25%, or less than 20%, or less than 10%, or less than 5%, or less than4%, or less than 3%, or less than 2%, or less than 1%, or in a rangefrom 0.25 to 0.75%, or less than 0.5%.

The open area fraction (or open area or Percentage of Open Area) of aconductive micropattern, or region of a conductive micropattern, is theproportion of the micropattern area or region area that is not shadowedby the conductor. The open area is equal to one minus the area fractionthat is shadowed by the conductor, and may be expressed conveniently,and interchangeably, as a decimal or a percentage. Area fraction that isshadowed by conductor is used interchangeably with the density of linesfor a micropatterned conductor. Micropatterned conductor is usedinterchangeably with electrically conductive micropattern and conductivemicropattern. Thus, for the values given in the above paragraph for thefraction shadowed by conductor, the open area values are greater than50%, greater than 75%, greater than 80%, greater than 90%, greater than95%, greater than 96%, greater than 97%, greater than 98%, greater than99%, 99.25 to 99.75%, 99.8%, 99.85%, 99.9% and even 99.95. In someembodiments, the open area of a region of the conductor micropattern(e.g., a visible light transparent conductive region) is between 80% and99.5%, in other embodiments between 90% and 99.5%, in other embodimentsbetween 95% and 99%, in other embodiments between 96% and 99.5%, inother embodiments between 97% and 98%, and in other embodiments up to99.95%. With respect to the reproducible achievement of useful opticalproperties (e.g. high transmission and invisibility of conductivepattern elements) and electrical properties, using practicalmanufacturing methods, preferred values of open area are between 90 and99.5%, more preferably between 95 and 99.5%, and in some embodimentsbetween 95 and 99.95%.

To minimize interference (e.g. with the pixel pattern of some displays)and to avoid viewability of the pattern elements (e.g., conductor lines)by the naked eye of a user or viewer, the minimum dimension of theconductive pattern elements (e.g., the width of a line or conductivetrace) should be less than or equal to approximately 50 micrometers, orless than or equal to approximately 25 micrometers, or less than orequal to approximately 10 micrometers, or less than or equal toapproximately 5 micrometers, or less than or equal to approximately 4micrometers, or less than or equal to approximately 3 micrometers, orless than or equal to approximately 2 micrometers, or less than or equalto approximately 1 micrometer, or less than or equal to approximately0.5 micrometer. In the design of one or more overlaid conductivemicropatterns, one may include concepts known in the art for minimizinginterference such as moiré effects between the one or more overlaidconductive micropatterns and the display pixels.

In some embodiments, the minimum dimension of conductive patternelements is between 0.5 and 50 micrometers, in other embodiments between0.5 and 25 micrometers, in other embodiments between 1 and 10micrometers, in other embodiments between 1 and 5 micrometers, in otherembodiments between 1 and 4 micrometers, in other embodiments between 1and 3 micrometers, in other embodiments between 0.5 and 3 micrometers,and in other embodiments between 0.5 and 2 micrometers. With respect tothe reproducible achievement of useful optical properties (e.g. hightransmission and invisibility of conductive pattern elements with thenaked eye) and electrical properties, and in light of the constraint ofusing practical manufacturing methods, preferred values of minimumdimension of conductive pattern elements are between 0.5 and 5micrometers, more preferably between 1 and 4 micrometers, and mostpreferably between 1 and 3 micrometers.

It has been found that certain arrangements of overlaid micropatternsresult in low visibility for the combination of micropatterns; whereasother arrangements result in high visibility for the combination ofmicropatterns.

FIGS. 5 a-5 c are illustrations depicting two layers of the same regularhexagonal mesh overlaid. The second micropattern is rotated relative tothe first micropattern at increasing angles, starting with 5 degrees forFIG. 5 a and increasing respectively from FIGS. 5 a to 5 c in 5 degreeincrements. In FIG. 5 a, an apparent composite pattern is presentwherein the center of each composite pattern has a diameter of at leastabout 4 cells. Hence, the apparent composite pattern has spatialdimensions greater than the dimensions of conductive features or thespacing between conductive features for either micropattern. Further,the apparent composite pattern typically has spatial dimensions greaterthan the repeat segment of the repeating geometry. In FIGS. 5 b- and 5c, the size of the apparent composite pattern is smaller, having acenter portion spanning about 3 and 2 cells in diameter, respectively.For illustration purposes, the individual linear traces of the meshes ofFIGS. 5 a-5 i are apparent and identifiable. The hexagonal cells arealso apparent and identifiable. However, when the pattern is amicropattern, the individual linear traces are not identifiable, nor arethe individual cells identifiable. However, the composite pattern thatwas created by the overlay of the micropatterns is highly visible (i.e.apparent), but not necessarily identifiable.

Particular designs and arrangements of overlaid conductive meshmicropatterns (e.g. with repeating cell geometry) can have lowvisibility when combined with periodically pixilated displays,particularly when certain designs are used. It is surmised that thevisibility can be even lower than some conductive mesh micropatternshaving random or pseudo-random cell geometry. Importantly, the designsand arrangement relate to reducing visibility when two conductivemicropatterns are overlaid.

In one embodiment of obtaining low visibility, the second conductivemicropattern overlays the first conductive micropattern such that atleast a portion of the linear traces of the second conductivemicropattern are non-parallel to the linear traces of first conductivemicropattern.

It is within the scope of this disclosure for the first and secondconductive micropatterns to be arranged intentionally with a specificrelative orientation. Two conductive micropatterns arranged with aspecific relative orientation can have a defined angle (or defined biasangle) with respect to each other. The angle of one conductivemicropattern with respect to second conductive micropattern is readilyevident when the two micropatterns comprise repeat segments having thesame geometry of cell(s). The following includes a procedure fordefining the bias angle for some embodiments. When the two micropatternscomprise repeat segments having the same geometry of cell(s), one candefine for the two micropatterns the same sets of equivalent directionsbased on the rotational symmetry of the single micropattern geometry themicropatterns share. For example, for a hexagonal mesh, six equivalentdirections can be selected, associated with the mesh geometry's six-foldrotational symmetry. As another example, for a square mesh, fourequivalent directions can be selected, associated with the meshgeometry's four-fold rotational symmetry. With such equivalentdirections defined in the same way for the two meshes, one has a basisfor defining or measuring the angle (i.e., bias angle or relativeorientation) between two conductive micropatterns. The angle between thetwo conductive micropatterns is the minimum angle separating equivalentdirections of the first conductive micropattern from the equivalentdirections of the second conductive micropattern. Still in the casewhere the two conductive micropatterns are mesh micropatterns having thesame repeat segment cell geometry, the visual appearance of thecombination of micropatterns will be periodic with respect to changingbias angle. The angular period of the changing visual appearance withincreasing bias angle will be equal to 360 degrees divided by the levelof rotational symmetry (1 for no rotational symmetry, 2 for two-foldrotational symmetry, 3 for three-fold rotational symmetry, 4-forfour-fold rotational symmetry, and 6 for six-fold rotational symmetry,for example). The term repeat angle is used herein to describe theangular period. Thus, unique (in terms of visual appearance) combinedgeometries for the combination of two conductive micropatternscomprising the same cell geometry will exist only over a range of anglesfrom 0 degrees to [360/level of rotational symmetry] degrees. Althoughthe combined geometry for the overlaid micropatterns is periodic withrespect to bias angle (with a repeat angle as just described), withrespect to the overall appearance of the combined micropatterns, it issometimes just as useful to define the bias angle with respect to onehalf of the repeat angle. This is because the overall visual appearancecan be the same for a bias angle of x as it is for a bias angle of[repeat angle minus x], for an x less than the one half the repeatangle. Thus, the full range of visual appearance of combinedmicropatterns can be defined within the bias angle range of zero degreesto one half of the repeat angle. It is useful in some cases to definethe bias angle between conductive micropatterns comprising the same meshgeometry as a fraction of the repeat angle. In some embodiments, thebias angle is between 0.1 to 0.9 times the repeat angle. In preferredembodiments, the bias angle is between 0.1 and 0.4 or between 0.6 and0.9 times the repeat angle. In other preferred embodiments, the biasangle is between 0.2 and 0.3 or between 0.7 and 0.8 times the repeatangle.

With reference to FIGS. 5 a-5 i, in one embodiment the second conductivemicropattern has linear traces that are non-parallel relative to thelinear traces of the first conductive micropattern by rotating thesecond micropattern relative to the first micropattern. The geometry ofthe first conductive micropattern is the same as the geometry of thesecond conductive micropattern. The geometry for both micropatterns is ahexagonal mesh with six-fold rotational symmetry. The repeat angle is 60degrees. The use of a relative bias angle is particularly useful whenthe first and second micropattern have the same cell (e.g. regular)geometry and the same cell dimension. It is also very useful to rotateone conductive micropattern comprising a regular cell geometry withrespect to a second conductive micropattern comprising the same regularcell geometry when the two micropatterns have cells of differentdimension. As the angle of rotation (bias angle) increases from about 5degrees (0.083 times the repeat angle), as depicted in FIG. 5 a to about15 degrees (0.25 times the repeat angle) as depicted in FIG. 5 c, thevisibility can be diminished. Although the angle of rotation can varydepending on the specific cell geometry and cell dimension, the angle ofrotation is preferably at least 10 degrees (as illustrated in FIG. 5 b)and less than 45 degrees (as illustrated in FIG. 5 i).

In another embodiment, the second conductive micropattern has lineartraces that are non-parallel to the linear traces of the firstconductive micropattern as a result of the second conductivemicropattern having a different cell geometry from the cell geometry ofthe first conductive micropattern. For example, with reference to FIG.6, the first conductive micropattern may have a square cell geometry andthe second conductive micropattern a hexagonal cell geometry, orvice-versa. Although, a portion of the linear traces of the square cellscan be parallel to the linear traces of the hexagon cells, a portion ofthe linear traces are non-parallel.

In another embodiment for obtaining low visibility, the secondconductive micropattern has a different cell dimension from the celldimension of the first conductive micropattern. The term cell dimensionrefers generally to the size of a cell of a mesh conductivemicropattern. For cells having the shape of regular polygons, it isconvenient to define (for the purpose of comparing the cell dimensionsof two conductive micropatterns) a cell dimension as the width of thecell, for example the edge length of a square cell, or as a furtherexample the separation between parallel faces of a hexagonal cell (alsoreferred to herein as the diameter or pitch of a hexagon).

In some embodiments, the average width or pitch of a regular cell formedfrom the conductive traces is typically no greater than 500 microns, 450microns, or 400 microns. In some preferred embodiments, both of themicropatterns have an average cell width no greater than 350 microns,300 microns, 250 microns, 200 microns, 150 microns, 100 microns, or 50microns.

For irregular cell shapes (or even for regular cell shapes), for thepurpose of comparing the cell dimensions of two mesh conductivemicropatterns having repeating cell geometries, a cell dimension can bedefined as the average length of all line segments (i.e., of allorientations) that pass through the centroid of the cell shape and thatextend in each direction to the boundary of the cell shape.

Two mesh conductive micropatterns having the same repeating cellgeometries may have different cell dimensions. Also, two mesh conductivemicropatterns having different repeating cell geometries may havedifferent cell dimensions. In some embodiments, the cell dimension ofthe first conductive micropattern is equal to between 1.1 and 6 timesthe cell dimension of the second conductive micropattern (i.e. ratios of1:1.1 to 1:6 respectively. It is preferred for the cell dimension of thefirst conductive micropattern to be equal to between 1.2 and 3 times thecell dimension of the second conductive micropattern, more preferablybetween 1.2 and 2.

In some preferred embodiments, the first conductive micropattern and thesecond conductive micropattern have the same repeating cell geometry,wherein the cell dimension of the first conductive micropattern isbetween 1.1 and 6 times the cell dimension of the second conductivemicropattern, and there is a bias angle between the patterns of between0.1 and 0.9 times the repeat angle. In some embodiments, the bias anglebetween the patterns of between 0.1 and 0.4 or between 0.6 and 0.9 timesthe repeat angle. In some of these embodiments, the repeating cellgeometry comprises regular polygons. In some of these embodiments, therepeating cell geometry is composed of a single regular polygon. In someof these embodiments, the repeating cell geometry is composed of regularhexagons.

In some preferred embodiments, the first conductive micropattern and thesecond conductive micropattern have the same repeating cell geometry,wherein the cell dimension of the first conductive micropattern isbetween 1.2 and 3 times the cell dimension of the second conductivemicropattern, and there is a bias angle between the patterns of between0.1 and 0.4 or between 0.6 and 0.9 times the repeat angle. In some ofthese embodiments, the repeating cell geometry comprises regularpolygons. In some of these embodiments, the repeating cell geometry iscomposed of a single regular polygon. In some of these embodiments, therepeating cell geometry is composed of regular hexagons.

In some preferred embodiments, the first conductive micropattern and thesecond conductive micropattern have the same repeating cell geometry,wherein the cell dimension of the first conductive micropattern isbetween 1.1 and 6 times the cell dimension of the second conductivemicropattern, and there is a bias angle between the patterns of betweenabout 10 degrees and about 45 degrees. In some embodiments, the celldimension of the first conductive micropattern is between 1.2 and 3times the cell dimension of the second conductive micropattern. In someof these embodiments, the repeating cell geometry comprises regularpolygons. In some of these embodiments, the repeating cell geometry iscomposed of a single regular polygon. In some of these embodiments, therepeating cell geometry is composed of regular hexagons.

The visibility of the overlaid micropattern can be determined by usingvarious methods. In some embodiments, the visibility of the overlaidmicropattern is determined by use of (i.e. human) test panels toevaluate the visibility (according to the method described in theexamples).

Although mathematical models such as described in “A Standard Model forFoveal Detection of Spatial Contrast” (Journal of Vision, 2005 5,717-740) have been used to evaluate the visibility of images havingsufficient dimension such that the images are apparent (i.e. readilyseen, visible) and identifiable (i.e. to ascertain definitivecharacteristics of) to the unaided human eye of normal (i.e. 20/20)vision, such mathematical model is not believed to have been adapted foruse to determine the visibility of non-apparent micropatterns oroverlaid micropatterns.

Accordingly, in other embodiments, a method of determining thevisibility of a patterned substrate is described comprising providing adigital image of a micropatterned substrate such as overlaidmicropatterns and calculating the spatial contrast threshold of thedigital image with a model for foveal detection (i.e. standard spatialobserver model).

Mathematical models can be favored relative to (i.e. human) test panelsfor a variety of reasons. Test panels are typically more subjective andgenerally require a multiple of participants to obtain a statisticallymeaningful result. Further, the use of test panels typically requiresthat actual samples be made of each of the micropatterns in order thatthe visibility can be evaluated.

The input for a mathematical model can also be generated by providing asample comprising (e.g. a light transparent) substrate and anon-transparent micropattern, simulating the lighting conditions of thesample when the sample is viewed during use; and digitally imaging thesample. However, the mathematical model can also utilize a digital imageof a digitally designed micropattern. Hence, is this embodiment, thevisibility of a micropattern or overlaid micropattern can be evaluatedwithout actually fabricating a physical sample. This is amenable to moreefficiently evaluating the visibility of a multitude of micropatternswithout actual fabrication thereof.

Regardless of whether, a (i.e. human) test panel or a mathematical modelis used, the digital image of the micropatterned substrate, or digitaldesign thereof, is typically cropped to include only the micropattern.Any edges or borders that arise as a result of cropping that are notactually present in the overlaid patterns should be omitted prior tocalculating the contrast thresholds. Although during transmission, (i.e.when the micropattern is viewed with backlighting transmitting throughthe substrate) the metal micropattern appears dark against a transparentbackground, in order to simulate the micropattern's appearance whenviewed with reflected light, it is preferred to digitally alter (such asby reversing the polarity of the image on a computer screen) such thatthe transparent substrate is dark and the micropattern is light.Different contrast threshold values may be computed by the model in theabsence of digitally altering the micropattern image in this manner.

The calculated contrast threshold described herein (as conducted asdescribed in the examples) have been found to correspond with thevisibility as determined by (i.e. human) test panels. When themicropattern or overlaid micropatterns have a contrast threshold of lessthan −35 decibels, the micropattern is most visible. Hence, the contrastthreshold is preferably greater than −35 decibels. When the contrastthreshold is greater than −30 decibels or −25 decibels, the micropattern(e.g. beat pattern of overlaid micropattern) is still apparent andidentifiable. However, when the micropattern or overlaid micropatternshas a predicted contrast threshold of greater than −24, −23, −22, −21 or−20 decibels, the micropattern or overlaid micropatterns becomessubstantially less visible. In preferred embodiments, the contrastthreshold is greater than −15 decibels, −10 decibels, or −5 decibels.When the micropattern or overlaid micropatterns has a predicted contrastthreshold of 0 or greater, the micropattern or overlaid micropattern isnot visible. As the contrast threshold increases, the uniformity inappearance of the sample increases. A difference in contrast thresholdvalues of 1 decibel is a ‘just noticeable difference’ to the averagehuman viewer.

The distance for calculating the contrast threshold can vary, yet ischosen to correlate with a viewing distance of interest, i.e. typicallythe average viewing distance of the micropatterned substrate duringordinary use. For example, if the article is a touch sensor display of acell phone, the normal viewing distance is typically about 280 mm to 300mm. This corresponds to a distance unit of the model of about 30000(i.e. 3000 foveal detection model distance units). In some embodiments,the preferred (e.g. overlaid) micropattern has the contrast thresholds,as described above, at less than 30000 distance units such as 25000 or20000 or 15000.

The sample size utilized in the calculation is generally of sufficientsize to be representative of the physical and/or designed sample. If theoverlaid pattern (the net pattern) is larger than the sample size butwithin a viewing area that would be covered by foveal viewing (i.e.,2.13 degrees of visual angle) at the desired viewing distance, oneshould obtain a sample that would subtend the fovea.

In general, the deposited electrically conductive material reduces thelight transmission of the touch sensor. Basically, wherever there iselectrically conductive material deposited, the display is shadowed interms of its viewability by a user. The degree of attenuation caused bythe conductor material is proportional to the area fraction of thesensor or region of the sensor that is covered by conductor, within theconductor micropattern.

In general, it is desirable for a transparent touch screen sensor toexhibit a low value of haze. Haze refers to a property related to thescattering of light as it passes through a medium, e.g. as measured by aHaze-Gard instrument (Haze-Gard plus, BYK Gardner, Columbia, Md.). Insome embodiments, the touch screen sensor exhibits haze less than 10%,in some embodiments less than 5%, in some embodiments less than 4%, insome embodiments less than 3%, in some embodiments less than 2%.

Embodiments are disclosed which achieve a desirable combination of hightransmission (also referred to as visible light transmittance), lowhaze, and low conductor trace visibility for regions including conductormicropatterns. The conductor micropatterns are thus especially usefulwhen used as part of a sensing area or region of a touch screen sensordisplay, e.g. when the micropattern overlays a viewable region of thedisplay.

In some embodiments, in order to generate a visible light transparentdisplay sensor that has uniform light transmission across the viewabledisplay field, even if there is a non-uniform distribution of sheetresistance, e.g. derived from a non-uniform mesh of conductive material,the sensors include isolated conductor deposits added to the conductormicropattern that serve to maintain the uniformity of lighttransmittance across the pattern. Such isolated conductor deposits arenot connected to the drive device (e.g., electrical circuit or computer)for the sensor and thus do not serve an electrical function.

Similar isolated conductive (e.g. metal) features can be added inregions of space between contiguous transparent conductive regions, e.g.contiguous transparent conductive regions that include micropatternedconductors in the form of two dimensional meshes or networks, in orderto maintain uniformity of light transmittance across the sensor,including the transparent conductive regions and the region of spacebetween them. In addition to isolated squares of conductor, other usefulisolated deposits of conductor for tailoring optical uniformity includecircles and lines. The minimum dimension of the electrically isolateddeposits (e.g., the edge length of a square feature, the diameter of acircular feature, or the width of a linear feature) is less than 10micrometers, less than 5 micrometers, less than 2 micrometers, or evenless than 1 micrometer.

With respect to the reproducible achievement of useful opticalproperties (e.g. high transmission and invisibility of conductivepattern elements), using practical manufacturing methods, the minimumdimension of the electrically isolated deposits is preferably between0.5 and 10 micrometers, more preferably between 0.5 and 5 micrometers,even more preferably between 0.5 and 4 micrometers, even more preferablybetween 1 and 4 micrometers, and most preferably between 1 and 3micrometers. In some embodiments, the arrangement of electricallyisolated conductor deposits is designed to lack periodicity. A lack ofperiodicity is preferred for limiting unfavorable visible interactionswith the periodic pixel pattern of an underlying display. For anensemble of electrically isolated conductor deposits to lackperiodicity, there need only be a single disruption to the otherwiseperiodic placement of at least a portion of the deposits, across aregion having the deposits and lacking micropattern elements that areconnected to decoding or signal generation and/or processingelectronics. Such electrically isolated conductor deposits are said tohave an aperiodic arrangement, or are said to be an aperiodicarrangement of electrically isolated conductor deposits. In someembodiments, the electrically isolated conductor deposits are designedto lack straight, parallel edges spaced closer than 10 micrometersapart, e.g. as would exist for opposing faces of a square deposit withedge length of 5 micrometers. More preferably the isolated conductordeposits are designed to lack straight, parallel edges spaced closerthan 5 micrometers apart, more preferably 4 micrometers apart, even morepreferably 3 micrometers apart, even more preferably 2 micrometersapart. Examples of electrically isolated conductor deposits that lackstraight, parallel edges are ellipses, circles, pentagons, heptagons,and triangles. The absence within the design of electrically isolatedconductor deposits of straight, parallel edges serves to minimizelight-diffractive artifacts that could disrupt the viewability of adisplay that integrates the sensor.

The impact of the conductor micropattern on optical uniformity can bequantified. If the total area of the sensor, and hence the conductormicropattern, that overlays a viewable region of the display issegmented into an array of 1 millimeter by 1 millimeter regions,preferred sensors include conductor micropatterns wherein none of theregions have a shadowed area fraction that differs by greater than 75percent from the average for all of the regions. More preferably, nonehave a shadowed area fraction that differs by greater than 50 percent.More preferably, none have a shadowed area fraction that differs bygreater than 25 percent. Even more preferably, none have a shadowed areafraction that differs by greater than 10 percent. If the total area ofthe sensor, and hence the conductor micropattern, that overlays aviewable region of the display is segmented into an array of 5millimeter by 5 millimeter regions, preferred sensors include conductormicropatterns wherein none of the regions have a shadowed area fractionthat differs by greater than 50 percent from the average for all of theregions. Preferably, none have a shadowed area fraction that differs bygreater than 50 percent. More preferably, none have a shadowed areafraction that differs by greater than 25 percent. Even more preferably,none have a shadowed area fraction that differs by greater than 10percent.

The disclosure allows for the use of metals as the conductive materialin a transparent conductive sensor, as opposed to transparent conductingoxides (TCO's), such as ITO.

Examples of useful metals for forming the electrically conductivemicropattern include gold, silver, palladium, platinum, aluminum,copper, nickel, tin, alloys, and combinations thereof.

Optionally, the conductor can also be a composite material, for examplea metal-filled polymer. The conductor can be reflective, as in the caseof thin film metal, for example silver, aluminum, etc. Alternatively,the conductor can be absorptive and appear dark or black, as in the caseof a carbon-filled composite conductor, for example as derived from aprintable carbon-based conductive ink. Furthermore, the conductor cancomprise multiple layers, for example the conductor may comprise a metallayer and an overlayer designed to reduce the reflectivity of the metalor to prevent corrosion of the metal, as is known in the art. Thisdisclosure is not limited with respect to the selection or design of thematerial that comprises the conductor. However, the concepts developedherein have been found to be particularly useful when reflectiveconductor patterns are needed or otherwise preferred.

In some embodiments, the (e.g. metal) micropattern is relatively thin,ranging in thickness from about 5 nanometers to about 50 nanometers. Inother embodiments, the (e.g. metal) micropattern has a thickness of atleast 60 nm, 70 nm, 80 nm, 90 nm, or 100 nm. In some embodiments, thethickness of the (e.g. metal) micropattern is at least 250 nm. In someembodiments, the micropattern is a silver micropattern have a thicknessof at least 300 nm, 400 nm, 500 nm, 600 nm, 700 nm, 800 nm, 900 nm, andeven 1000 nm or greater. The other embodiments, the micropattern is agold micropattern having a thickness of at least 300 nm, 350 nm, 400 nm,or greater. Metal micropatterns of increased thickness can be preparedas described in 61/220,407, filed Jun. 25, 2009; incorporated herein byreference.

In preferred embodiments, the (e.g. metal) conductive micropatternedsubstrates are suitable for use in electronic displays. Electronicdisplays include reflective displays and displays with internal sourcesof light. Electronic displays with internal sources of light includeilluminated displays. By “illuminated” it is meant “brightened by lightor emitting light”. The illuminated display may be a liquid crystaldisplay having a backlighting or edge lighting light source that may beexternal to the core liquid crystal panel but internal to the displaydevice overall. Or the illuminated display may be an emissive displaysuch as a plasma display panel (PDP) or organic light emitting diode(OLED) display. Reflective displays include electrophoretic displays,electrowetting displays, electrochromic displays, and reflectivecholesteric liquid crystal displays. The micropatterned substrates ofthe invention are especially useful as part of an illuminated electronicdisplay.

Conductor micropatterns according to the invention can be generated byany appropriate patterning method, e.g. methods that includephotolithography with etching or photolithography with plating (see,e.g., U.S. Pat. No. 5,126,007; U.S. Pat. No. 5,492,611; U.S. Pat. No.6,775,907). Additionally, the conductor patterns can be createdutilizing on one of several other exemplary methods including lasercured masking, inkjet printing, gravure printing, and microreplication;each of which are known in the art and described in greater detail inU.S. Publication No. US2009/0219257; incorporated herein by reference.In some embodiments, the conductive (e.g. metal) micropatterns areprepared via microcontact printing, such as described in 61/220,407,filed Jun. 25, 2009; incorporated herein by reference.

The two-dimensional conductive micropattern can be designed to achieveanisotropic or isotropic sheet resistance in a conductive region (e.g.,a visible light transparent conductive region) of the sensor, such asdescribed in U.S. Publication No. US2009/0219257; incorporated herein byreference. By anisotropic sheet resistance, what is meant is that themagnitude of the sheet resistance of the conductive micropattern isdifferent when measured or modeled along two orthogonal directions. Byisotropic sheet resistance, what is meant is that the magnitude of thesheet resistance of the conductive micropattern is the same whenmeasured or modeled along any two orthogonal directions in the plane, asin the case for a square grid formed with traces of constant width forboth directions.

In some embodiments, transparent conductive regions with different sheetresistance in at least one direction are created by including selectivebreaks in conductive traces within an otherwise continuous and uniformmesh. This approach of selective placement of breaks is especiallyuseful for generating articles including patterns of visible transparentconductive regions where the optical transmittance across the article isuniform. The starting mesh can be isotropic or anisotropic.

In other embodiments that include selective breaks in an otherwisecontinuous and uniform mesh, the breaks can be placed in order to createapproximately continuously varying sheet resistance in a givendirection. In some embodiments, two transparent conductive regions withdifferent sheet resistance in at least one direction are created byincluding in each of the two regions a contiguous mesh with its owndesign, each mesh not necessarily including selectively placed breaks.Examples of two meshes with designs that lead to different values ofsheet resistance for current passing in a single direction, e.g. the xdirection in FIG. 2, include two meshes with the same thickness(dimension in the z direction in FIG. 2) of the same conductive materialdeposit but with different amounts with current-carrying cross-sectionalarea (y-z plane in FIG. 2) per unit width in the y direction. Oneexample of such a pair of mesh regions are two square grid regions eachcomprising conductive traces of width 2 micrometers but with differentpitch, e.g. 100 micrometers and 200 micrometers. Another example of sucha pair of mesh regions are two rectangular grid regions (non-square,with 100 micrometer pitch in the one direction and 200 micrometer pitchin the orthogonal direction) each comprising conductive traces of width2 micrometers but with different orientation, e.g. with the long axes ofthe rectangular cells in the first regions oriented at 90 degrees withrespect to the rectangular cells in the second region.

In some embodiments, the sensors include an insulating visible lighttransparent substrate layer that supports a pattern of conductor, thepattern includes a visible light transparent micropattern region and aregion having a larger feature that is not transparent, wherein thevisible light transparent micropattern region and the larger featureregion include a patterned deposit of the same conductor (e.g., a metal)at approximately the same thickness. The larger feature can take theform of, e.g., a wide conductive trace that makes contact to a visiblelight transparent conductive micropattern region or a pad for makingcontact with an electronic decoding, signal generation, or signalprocessing device. The width of useful larger features, in combinationon the same insulating layer with visible light transparent conductivemicropattern regions, is e.g. between 25 micrometers and 3 millimeters,between 25 micrometers and 1 millimeter, between 25 micrometers and 500micrometers, between 25 micrometers and 250 micrometers, or between 50micrometers and 100 micrometers.

Examples

The following describe exemplary touch screen sensor designs. They canbe fabricated using known photolithographic methods, e.g. as describedin U.S. Pat. No. 5,126,007 or U.S. Pat. No. 5,492,611. The conductor canbe deposited using physical vapor deposition methods, e.g. sputtering orevaporation, as is known in the art. Unless otherwise noted, theexamples below include conductors patterned by a micro-contact printingtechnique (see technique description above and also co-pending US PatentPublication No. US2009/0218310). Each conductive pattern exemplifiedherein is useful as a transparent touch screen sensor, when connected todecoding circuitry, as is known in the art (e.g., U.S. Pat. No.4,087,625; U.S. Pat. No. 5,386,219; U.S. Pat. No. 6,297,811; WO2005/121940 A2).

Visibility of Overlaid Micropatterned Substrates Predicted with theStandard Spatial Observer Model

The contrast thresholds of the overlaid micropatterned substrates ofComparative Example A, Example B and Examples 1-25 (unless specifiedotherwise) were calculated using a version of the mathematical model“Standard A” described in “A Standard Model for Foveal Detection ofSpatial Contrast” (Journal of Vision, 2005 5, 717-740). The Standard Amodel was implemented using Matlab version 7.7.0.471 (R2008b) on aHewlett-Packard xw8400 workstation using the following parameters.

Parameter Fit Value A - Gain 373.08 α 0.8493 p .7786 f₀ 4.1726(cycles/deg) f₁ 1.3625 (cycles/deg) β 2.4081 σ 0.6273

The definition of the above parameters are described in Appendix C and Dat pp. 736-737 of “A Standard Model for Foveal Detection of SpatialContrast” (Journal of Vision, 2005 5, 717-740).

Analyses were conducted assuming a square pixel size of 0.265 mm, andthe nominal mean grayscale value in the image was estimated for eachfoveal block analyzed.

The micropattern analysis was accomplished by:

1. First creating the desired pattern covering at least a fewcentimeters expanse to allow for later image cropping, using a computeraided drafting or design (CAD) software package (e.g., L-Edit,commercially available from Tanner EDA, a division of Tanner ResearchInc., Monrovia, Calif.), and saving the file in the .gds format.

2. The .gds files were then converted to PDF (Portable Document Format)format and saved.

3. Next the PDF files were opened in Adobe Illustrator (Adobe Systems,Inc.; CS2, 12.0.0) and were cropped to include only the micropatternedarea.

4. The polarity of the digital image was then reversed such that thebackground was black and the micropattern was white.

5. The file was again saved in the PDF format.

6. The new PDF file was opened in Adobe Photoshop (Adobe Systems, Inc.;Version 5.5) with maximum image resolution of 9999 pixels per inch. Theanti-aliasing option was not selected, so that the images remained allblack or white (no intermediate gray levels).

7. This digital image was then saved as a TIFF (Tagged Image FileFormat) and then cropped in Matlab to a size of 3,000×3,000 pixels.

The contrast thresholds were then calculated for a viewing distance of30000 units of distance according to the model which is equivalent toabout 28-30 cm.

Comparative Example A

A transparent sensor element 400 for a touch screen sensor isillustrated in FIG. 8. The sensor element 400 includes two patternedconductor layers 410, 414, (e.g., an X axis layer and a Y axis layer)two optically clear adhesive layers 412, 416, and a base plate 418,laminated together and depicted as separated in FIG. 8 for clarity.Layers 410 and 414 include transparent conductive mesh bars where onelayer is oriented in the x axis direction and the other layer isorientated in the y axis direction, with reference to FIG. 2. The baseplate 418 is a sheet of glass measuring 6 centimeter by 6 centimeters inarea and 1 millimeter in thickness. A suitable optically clear adhesiveis Optically Clear Laminating Adhesive 8141 from 3M Company, St. Paul,Minn. For each of the X-layer and the Y-layer, a clear polymer film witha micropattern of metal is used. A micropattern of thin film goldaccording to the following description is deposited onto a thin sheet ofPET. Suitable PET substrates include ST504 PET from DuPont, Wilmington,Del., measuring approximately 125 micrometers in thickness.

The micropattern 440 is depicted in FIG. 9 and FIG. 10. The thickness ofthe gold is about 100 nanometers. The micropattern has transparentconductive regions in the form of a series of parallel mesh bars 442. Inaddition to mesh bars that are terminated with square pads 460(approximately 2 millimeters by 2 millimeters in area, comprisingcontinuous conductor in the form of thin film gold with thicknessapproximately 100 nanometers) for connection to an electronic device forcapacitive detection of finger touch to the base plate, there are meshbars 441 that are electrically isolated from the electronic device. Theisolated mesh bars 441 serve to maintain optical uniformity across thesensor. Each bar is comprised of a mesh made up of narrow metallictraces 443, the traces 443 measuring approximately 5 micrometers inwidth. The mesh bars each measure approximately 2 millimeters in widthand 66 millimeters in length. Within each mesh bar are rectangular cellsmeasuring approximately 0.667 millimeters in width and 12 millimeters inlength. This mesh design serves to provide ties between long-axis tracesin each mesh bar, to maintain electrical continuity along the mesh bar,in case of any open-circuit defects in the long axis traces. However, asopposed to the use of a square mesh with 0.667 millimeter pitch havingsuch ties, the rectangular mesh of FIG. 9 and FIG. 10 trades off sheetresistance along the mesh bar with optical transmittance more optimally.More specifically, the mesh bar depicted in FIG. 9 and FIG. 10 and a 2millimeter wide mesh bar comprising a square mesh with 0.667 millimeterpitch would both have essentially the same sheet resistance along thelong axis of the mesh bar (approximately 50 ohms per square); however,the square grid would occlude 1.5% of the area of the transparentconductive region and the mesh depicted in FIG. 9 and FIG. 10 occludesonly 0.8% of the area of the transparent conductive region.

The overlaid micropattern is illustrated in FIG. 36. The contrastthreshold at a distance of 30000 units (with pixel size of 0.265) ofComparative Example A was determined to be −41.4.

Example B

A transparent sensor element was fabricated and combined with a touchsensor drive device as generally shown in FIGS. 11, 12 and 13 usingmicrocontact printing and etching as described in co-assigned U.S.Provisional application 61/032,273, filed Feb. 28, 2008. The device wasthen integrated with a computer processing unit connected to a displayto test the device. The device was able to detect the positions ofmultiple single and or simultaneous finger touches, which was evidencedgraphically on the display. This example used micro-contact printing andetching techniques (see also co-pending U.S. Patent App. No. 61/032,273,filed Feb. 28, 2008) to form the micro-conductor pattern used in thetouch sensor.

Formation of a Transparent Sensor Element

First Patterned Substrate

A first visible light substrate made of polyethylene terephthalate (PET)having a thickness of 125 micrometers (μm) was vapor coated with 100 nmsilver thin film using a thermal evaporative coater to yield a firstsilver metalized film. The PET was commercially available as productnumber ST504 from E.I. du Pont de Nemours, Wilmington, Del. The silverwas commercially available from Cerac Inc., Milwaukee, Wis. as 99.99%pure 3 mm shot.

A first poly(dimethylsiloxane) stamp, referred to as PDMS andcommercially available as product number Sylgard 184, Dow Chemical Co.,Midland, Mich., having a thickness of 3 mm, was molded against a 10 cmdiameter silicon wafer (sometimes referred to in the industry as a“master”) that had previously been patterned using standardphotolithography techniques. The PDMS was cured on the silicon wafer at65° C. for 2 hours. Thereafter, the PDMS was peeled away from the waferto yield a first stamp having two different low-density regions withpatterns of raised features, a first continuous hexagonal mesh patternand a second discontinuous hexagonal mesh pattern. That is, the raisedfeatures define the edges of edge-sharing hexagons. A discontinuoushexagon is one that contains selective breaks in a line segment. Theselective breaks had a length less than 10 μm. The breaks were designedand estimated to be approximately 5 μm. In order to reduce theirvisibility, it found that, preferably, the breaks should be less than 10μm, more preferably, 5 μm or less, e.g., between 1 and 5 μm. Each raisedhexagon outline pattern had a height of 2 μm, had 1% to 3% areacoverage, corresponding to 97% to 99% open area, and line segments thatmeasured from 2 to 3 μm in width. The first stamp also included raisedfeatures defining 500 μm wide traces. The first stamp has a firststructured side that has the hexagonal mesh pattern regions and thetraces and an opposing second substantially flat side.

The stamp was placed, structured side up, in a glass Petri dishcontaining 2 mm diameter glass beads. Thus, the second, substantiallyflat side was in direct contact with the glass beads. The beads servedto lift the stamp away from the base of the dish, allowing the followingink solution to contact essentially all of the flat side of the stamp. A10 millimolar ink solution of 1-octadecanethiol (product number C18H3CS,97%, commercially available from TCI America, Portland Oreg.) in ethanolwas pipetted into the Petri dish beneath the stamp. The ink solution wasin direct contact with the second substantially flat side of the stamp.After sufficient inking time (e.g., 3 hours) where the ink has diffusedinto the stamp, the first stamp was removed from the petri dish. Theinked stamp was placed, structured side up, onto a working surface. Thefirst silver metalized film was applied using a hand-held roller ontothe now inked structured surface of the stamp such that the silver filmwas in direct contact with the structured surface. The metalized filmremained on the inked stamp for 15 seconds. Then the first metalizedfilm was removed from the inked stamp. The removed film was placed forthree minutes into a silver etchant solution, which contained (i) 0.030molar thiourea (product number T8656, Sigma-Aldrich, St. Louis, Mo.) and(ii) 0.020 molar ferric nitrate (product number 216828, Sigma-Aldrich)in deionized water. After the etching step, the resulting firstsubstrate was rinsed with deionized water and dried with nitrogen gas toyield a first patterned surface. Where the inked stamp made contact withthe silver of the first metalized substrate, the silver remained afteretching. Thus silver was removed from the locations where contact wasnot made between the inked stamp and silver film.

FIGS. 11, 11 a and 11 b show a first patterned substrate 700 having aplurality of first continuous regions 702 alternating between aplurality of first discontinuous regions 704 on a first side of thesubstrate, which is the side that contained the now etched and patternedsilver metalized film. The substrate has an opposing second side that issubstantially bare PET film. Each of the first regions 702 has acorresponding 500 μm wide conductive trace 706 disposed at one end. FIG.11 a shows an exploded view of the first region 702 having a pluralityof continuous lines forming a hexagonal mesh structure. FIG. 11 b showsan exploded view of the first discontinuous region 704 having aplurality of discontinuous lines (shown as selective breaks in eachhexagon) forming a discontinuous hexagonal mesh structure. Each meshstructure of regions 702 and 704 had 97% to 99% open area. Each linesegment measured from 2 to 3 μm.

Second Patterned Substrate

The second patterned substrate was made as the first patterned substrateusing a second visible light substrate to produce a second silvermetalized film. A second stamp was produced having a second continuoushexagonal mesh pattern interposed between a second discontinuoushexagonal mesh pattern.

FIGS. 12, 12 a and 12 b show a second patterned substrate 720 having aplurality of second continuous regions 722 alternating between aplurality of second discontinuous regions 724 on a first side of thesecond substrate. Each of the second regions 722 has a corresponding 500μm wide second conductive trace 726 disposed at one end. FIG. 12 a showsan exploded view of one second region 722 having a plurality ofcontinuous lines forming a hexagonal mesh structure. FIG. 12 b shows anexploded view of one second discontinuous region 724 having a pluralityof discontinuous lines (shown as selective breaks in each hexagon)forming discontinuous hexagonal mesh structure. The selective breaks hada length less than 10 μm. The breaks were designed and estimated to beapproximately 5 μm. In order to reduce their visibility, it found that,preferably, the breaks should be less than 10 μm, more preferably, 5 μmor less, e.g., between 1 and 5 μm. Each mesh structure of region 722 and724 had 97% to 99% open area. Each line segment measured from 2 to 3 μm.

Further with respect to the geometries, orientations, and celldimensions of the mesh designs of the first and second patternedsubstrates, the first patterned substrate comprised hexagonal cells withdiameter of 300 micrometers and the second pattern substrate comprisedhexagonal cells with diameter of 200 micrometers. One of the conductormicropatterns had a cell dimension of 1.5 times the cell dimension ofthe second conductor micropattern. In the sensor element describedbelow, as formed in part by the combination of the two patternedsubstrates, there was a relative orientation or bias angle between thehexagonal meshes of 30 degrees. The bias angle between the two conductormicropatterns was 0.5 times the repeat angle of 60 degrees for ahexagonal mesh.

Formation of a Projected Capacitive Touch Screen Sensor Element

The first and second patterned substrates made above were used toproduce a two-layer projected capacitive touch screen transparent sensorelement as follows.

The first and second patterned substrates were adhered together usingOptically Clear Laminating Adhesive 8141 from 3M Company, St. Paul,Minn. to yield a multilayer construction. A handheld roller was used tolaminate the two patterned substrates with the regions of the first andsecond conductive trace regions 706 and 726 being adhesive free. Themultilayer construction was laminated to a 0.7 mm thick float glassusing Optically Clear Laminating Adhesive 8141 such that the first sideof the first substrate was proximate to the float glass. The adhesivefree first and second conductive trace regions 706 and 726 allowedelectrical connection to be made to the first and second patternedsubstrates 700 and 720.

FIG. 13 shows a top plan view of a multilayer touch screen sensorelement 740 where the first and second patterned substrate have beenlaminated. Region 730 represented the overlap of the first and secondcontinuous regions. Region 732 represented the overlap of the firstcontinuous region and the second discontinuous region. Region 734represented the overlap of the second continuous region and the firstdiscontinuous region. And, region 736 represented the overlap betweenthe first and second discontinuous regions. While there was a pluralityof these overlap regions, for ease of illustration, only one region ofeach has been depicted in the figure.

The integrated circuits used to make mutual capacitance measurements ofthe transparent sensor element were PIC18F87J10 (Microchip Technology,Chandler, Ariz.), AD7142 (Analog Devices, Norwood, Mass.), andMM74HC154WM (Fairchild Semiconductor, South Portland, Me.). ThePIC18F87J10 was the microcontroller for the system. It controlled theselection of sensor bars which MM74HC154WM drives. It also configuredthe AD7142 to make the appropriate measurements. Use of the systemincluded setting a number of calibration values, as is known in the art.These calibration values can vary from touch screen to touch screen. Thesystem could drive 16 different bars and the AD7142 can measure 12different bars. The configuration of the AD7142 included selection ofthe number of channels to convert, how accurately or quickly to takemeasurements, if an offset in capacitance should be applied, and theconnections for the analog to digital converter. The measurement fromthe AD7142 was a 16 bit value representing the capacitance of the crosspoint between conductive bars in the matrix of the transparent sensorelement.

After the AD7142 completed its measurements it signaled themicrocontroller, via an interrupt, to tell it to collect the data. Themicrocontroller then collected the data over the SPI port. After thedata was received, the microcontroller incremented the MM74HC154WM tothe next drive line and cleared the interrupt in the AD7142 signaling itto take the next set of data. While the sampling from above wasconstantly running, the microcontroller was also sending the data to acomputer with monitor via a serial interface. This serial interfaceallowed a simple computer program, as are known to those of skill in theart, to render the raw data from the AD7142 and see how the values werechanging between a touch and no touch. The computer program rendereddifferent color across the display, depending on the value of the 16 bitvalue. When the 16 bit value was below a certain value, based on thecalibration, the display region was rendered white. Above thatthreshold, based on the calibration, the display region was renderedgreen. The data were sent asynchronously in the format of a 4 byteheader (0xAAAAAAAA), one byte channel (0x00-0x0F), 24 bytes of data(represents the capacitive measurements), and carriage return (0x0D).

Results of Testing of the System

The transparent sensor element was connected to the touch sensor drivedevice. When a finger touch was made to the glass surface, the computermonitor rendered the position of touch that was occurring within thetouch sensing region in the form of a color change (white to green) inthe corresponding location of the monitor. When two finger touches weremade simultaneously to the glass surface, the computer monitor renderedthe positions of touches that were occurring within the touch sensingregion in the form of a color change (white to green) in thecorresponding locations of the monitor. When three finger touches weremade simultaneously to the glass surface, the computer monitor renderedthe positions of touches that were occurring within the touch sensingregion in the form of a color change (white to green) in thecorresponding locations of the monitor.

Preparation of Additional Two-Layer Meshes

Samples of microcontact printed meshes were prepared as described inU.S. Provisional Application Ser. No. 61/221,888, filed Jun. 30, 2009.

Two-layer mesh samples were prepared as follows: single layers ofmicropatterned meshes approximately 1.7 cm×1.7 cm were laminated to eachother using 3M Optically Clear Adhesive 8271 (3M Company, Maplewood,Minn.), one layer being rotated a specified number of degrees from theother layer, and the centers of both layers being located over oneanother (the specifics of each overly arrangement is further describedin the following table). The two-layer construction was then laminatedto the center of a 2 inch×3 inch×1 mm glass microscope slide using thesame optically clear adhesive. The silver patterned side of each layerfaced the glass slide. Seven two-layer mesh samples were prepared forvisibility studies, as well as two “blank” samples constructed in thesame way as the mesh samples, but using unpatterned 5 mil PET (ST504,E.I. DuPont de Nemours and Company, Wilmington, Del.) for each of thetwo layers. The sample set prepared for visibility testing is shownbelow.

Visibility of Overlaid Micropatterned Substrates as Determined with TestPanel

A viewing device was constructed in which a participant (“viewer”) wasseated in front of a viewing port. Behind the viewing port and containedwithin an enclosure was a light source and a sample holder. A singlesample was mounted in a black sample holder positioned approximately 25cm below the light source (30 watt bulb) and tilted towards the viewerat an approximately 7 deg angle. The sample holder masked the microscopeslide except for a 1.4 cm×1.4 cm square aperture through which thetwo-layer samples could be seen by the viewer. Hence, the sample sizeviewed by the test panel covered a larger surface area than the samplesize used for determining the contrast threshold. The sample holder wasinserted into an aperatured stage within a chamber. The viewing distancebetween the sample and the viewer's eyes was 280 mm to 320 mm. Thechamber was darkened on the other side of the aperture allowing theviewer to look through the layers of the mesh pattern, the mountingglass, and into the darkened viewing box beyond—so as to simulatelooking at the surface of a display with the backlighting illuminationturned off with ambient light reflecting off the surface of the display.The light source was connected to a Powerstat® Variable Autotransformer(Type 3PN116C, 120 V in, 0-140 V out, 10 Å, The Superior ElectricCompany, Bristol, Conn.) which allowed viewers to adjust the amount oflight illuminating the sample.

The Method of Adjustment paradigm (Psychophysics: The fundamentals,Gescheider, G. A., Lawrence Erlbaum Associates, Inc. Mahwah, N.J.(1997)) was used to measure visibility of the samples as follows: Theroom lights were turned off. A sample was placed in the aperture of thesample holder and inserted into the viewing device. The viewer placedtheir head in the viewing port such that they could see the sample, butdirect reflection of the light bulb was not visible. The viewer wasinstructed to begin with the light source dark (variable autotransformerdial set at 0) and increase the amount of light by turning the dialuntil the pattern of the sample was just barely able to be seen (TestMethod A). Some viewers were told to begin with the light source at fullstrength (variable autotransformer dial set at 140) and decrease theamount of light until the pattern of the sample is just barely able tobe seen (Test Method B). Test Method A was used for half of the totalnumber of measurements made by each viewer, and Test Method B was usedfor the other half of the total number of measurements made by eachviewer. Each of the samples were measured twice per viewer using testMethod A and twice per viewer using Test Method B. A mean value was thencalculated for each viewer. For half of the viewers, Method A was usedfirst for each of the samples followed by Method B; whereas for theother half of the viewers Method B was used first and then Method A. Thesample order was randomized. Viewers were instructed that they may notbe able to see a pattern on one or several samples, or may be able tosee a pattern in all samples. The number corresponding to the positionof the variable autotransformer dial at which point the viewer was ableto just barely see the pattern of a sample was the value recorded forthe purpose of ranking the apparent visibilities. For each sample, amean value was then calculated based on all the mean values of theviewers. Statistical outliers (i.e. more than 3 standard deviations)were omitted.

The rank order of the visibilities of the two-layer samples was comparedto the predicted rank order as calculated by the model. The comparisonof rank order is shown below.

TABLE 1 First Conductive Micropattern Second Conductive MicropatternOverlaid Cell Trace (i.e. Cell Trace (i.e. Cell Bias MicropatternDimension* line) Width Dimension* line) Width Dimension Angle Sample(microns) (microns) (microns) (microns) Ratio (deg) 1 (FIG. 14) 100 2600 2 6 30 2 (FIG. 15) 200 2 600 2 3 30 3 (FIG. 16) 400 2 600 2 1.5 30 4(FIG. 17) 300 2 600 2 2 0 5** (FIG. 7) 200 2 300 2 1.5 30 Example B 6(FIG. 18) 100 2 100 2 1 30 7 (FIG. 19) 600 2 600 2 1 30 8 Control Ablank NA blank NA NA 30 9 Control B blank NA blank NA NA 30 *Hexface-to-face distance **It was found that the overlaid micropattern ofExample 5 (FIG. 7) had a bias angle of 27 degrees.

TABLE 2 Contrast Thresholds at Distance Sample 30000 units Order asSample Order (with pixel Determined as Determined size of .265 mm) byModel by Test Panel Visibility −35.2 7 7 Most visible −31.7 3 3 | −26.14 2 | −29.0 2 4 | −21.0 1 1 ↓ −17.0 (30° bias angle) −17.0 (27° biasangle) 5 5 Least visible    1.7 6 6 Not visible N/A 8 8 Not visible -Control A (no micropattern) N/A 9 9 Not visible - Control B (nomicropattern)

In the case of CAD generated overlaid micropatterns and those that wouldbe produced in manufacture, the micropatterns can be overlaid preciselyresulting in a regular net pattern. However, when the micropatterns areoverlaid by hand, a small degree of positioning error can occur (1-2degrees). When the patterns are overlaid at an angle, such as in thecase of Example 5, such positioning error does not significantly affectthe calculated contrast thresholds. However, when the patterns areoverlaid by hand at a bias angle of 0, such small positioning errors canresult in an irregular pattern. Since the contrast threshold wascalculated on only a portion of the pattern, it may not berepresentative of the entire pattern, as was viewed by the test panel.This is believed to be the cause of the discrepancy between the sampleorder as determined by the model and the sample order as determined bythe test panel in connection with Sample 4.

Overlaid micropattern Samples 10-25 were digitally designed.

TABLE 3a First Conductive Micropattern Trace (i.e. line) Cell Dimension*Width Sample (microns) (microns) Cell Geometry 10 105 5 Square 11 105 5Square 12 105 5 Square 13 105 5 Square 14 300 5 Hexagon 15 300 5 Hexagon16 300 5 Hexagon 17 600 3 Hexagon 18 600 3 Hexagon 19 600 3 Hexagon 20300 3 Hexagon 21 200 3 Hexagon 22 300 3 Hexagon 23 133 2 Hexagon 24 6003 Hexagon 25 200 2 Hexagon *Hex face-to-face distance or square edgelength

TABLE 3b Second Conductive Micropattern Cell Trace (i.e.) CellDimension * Line Width Cell Dimension Sample (microns) (microns)Geometry Ratio 10 105 5 Square 1 11 105 5 Square 1 12 105 5 Square 1 13105 5 Square 1 14 300 5 Hexagon 1 15 300 5 Hexagon 1 16 300 5 Hexagon 117 600 3 Hexagon 1 18 600 3 Hexagon 1 19 600 3 Hexagon 1 20 50 3 Square6 21 80 3 Square 2.5 22 160 3 Square 1.875 23 133 2 Hexagon 1 24 600 3Hexagon 1 25 300 2 Hexagon 1.5 Sample of Table 3a Overlaid with Sampleof Table 3b Bias Angle (deg) Illustration Contrast Thresholds 10 45 FIG.20 −11.3 11 30 FIG. 21 −10.9 12 15 FIG. 22 −11.5 13 5 FIG. 23 −16.5 1445 FIG. 24 −22.7 15 15 FIG. 25 −22.4 16 5 FIG. 26 −22.4 17 45 FIG. 27−35.3 18 15 FIG. 28 −35.1 19 5 FIG. 29 −34.4 20 30 FIG. 30 Infinite(i.e., uniform appearance) 21 30 FIG. 31 −8.5 22 30 FIG. 32 −17.4 23 0FIG. 33 −3.9 24 0 FIG. 34 −38.2 25 0 FIG. 35 −17.7

What is claimed is:
 1. A touch screen sensor, comprising: a firstconductive mesh comprising a plurality of first conductive tracesforming an array of first cells including open areas, the first cellshaving a first cell geometry; and a second conductive mesh overlaid onand electrically isolated from the first conductive mesh, and comprisinga plurality of second conductive traces forming an array of second cellsincluding open areas, the second cells having a second cell geometrydifferent from the first cell geometry.
 2. The touch screen sensor ofclaim 1 wherein at least portions of the first and second cells havedifferent dimensions.
 3. The touch screen sensor of claim 1 wherein atleast portions of the first and second conductive traces arenon-parallel to one another.
 4. The touch screen sensor of claim 1wherein the first conductive mesh has more open areas than the secondconductive mesh.
 5. The touch screen sensor of claim 1, wherein thefirst conductive mesh has a first translational symmetry and the secondconductive mesh has a different second translational symmetry.
 6. Thetouch sensor of claim 5 wherein at least one of the first conductivemesh and the second conductive mesh comprises a repeating cell geometrythat comprises two or more different cell geometries, wherein a repeatsegment is present that can be translated in at least one direction. 7.The touch screen sensor of claim 1, wherein at least one of the firstand second conductive traces comprises wavy traces.
 8. The touch screensensor of claim 1 wherein the first and second conductive meshes eachcomprise a regular cell geometry.
 9. The touch screen sensor of claim 1wherein the first conductive mesh comprises a row and the secondconductive mesh comprises a column.
 10. The touch screen sensor of claim1 wherein a combination of the first and second conductive meshes has acontrast threshold at a distance of 30000 foveal detection modeldistance units of greater than −35 decibels.
 11. A touch screen sensor,comprising: a first conductive mesh having a first cell dimension; asecond conductive mesh overlaid on and electrically isolated from thefirst conductive mesh, and having a second cell dimension different fromthe first cell dimension.
 12. The touch screen sensor of claim 11wherein the first and second conductive meshes each comprise a regularcell geometry.
 13. The touch screen sensor of claim 11 wherein thesecond conductive mesh is oriented at a bias angle ranging from about 15degrees to about 40 degrees relative to the first conductive mesh. 14.The touch screen sensor of claim 11 wherein the first and secondconductive meshes differ in cell dimension by a ratio up to 1:6.
 15. Thetouch screen sensor of claim 11 wherein the first and second conductivemeshes have the same cell geometry, at least a portion of the secondconductive mesh is non-parallel to the first conductive mesh, and thereis a bias angle between the first conductive mesh and second conductivemesh of between about 0.1 and about 0.9 times the repeat angle.
 16. Thetouch screen sensor of claim 11 comprising a plurality of electricallyconductive rows and a plurality of electrically conductive columns,wherein each row comprises the first conductive mesh and each columncomprises the second conductive mesh.
 17. The touch screen sensor ofclaim 11 wherein a combination of the first and second conductive mesheshas a contrast threshold at a distance of 30000 foveal detection modeldistance units of greater than −35 decibels.
 18. A touch screen sensor,comprising: a first conductive mesh comprising a plurality of firstcells, each first cell formed by a plurality of first conductive traces;a second conductive mesh overlaid on the first conductive mesh andcomprising a plurality of second cells, each second cell formed by aplurality of second conductive traces, such that for at least one firstcell and one second cell, each first conductive trace of the first cellis non-parallel to each second conductive trace of the second cell. 19.An article comprising a first conductive mesh having a first geometryoverlaid on a second conductive mesh having a different second geometry,the first mesh oriented relative to the second mesh to minimize avisibility of the article.
 20. The article of claim 19, wherein thefirst mesh is oriented relative to the second mesh by rotating one ofthe first and second meshes relative to the other.